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Plant soybeans early to pump up yields

Early-planted soybeans can provide profitable yield advantages in most cases. “Plant soybeans early, but do it right,” recommends University of Nebraska-Lincoln soybean expert James E. Specht.

Jun 19, 2012

Plant soybeans early to pump up yields

By JIM CARLTON

Early-planted soybeans can provide profitable yield advantages in most cases. “Plant soybeans early, but do it right,” recommends University of Nebraska-Lincoln soybean expert James E. Specht.

His research has shown that for each day soybean planting was delayed after May 1, the yield penalty per day was as much as 0.63 bushel per acre in a “great” soybean year, such as the 2004 season, and 0.25 bushel per acre in a “not so great” soybean year, such as the 2003 season.

At a glance

• Research from UNL, other universities verifies advantages of early planting.

• More sunlight and more nodes are among the reasons researchers cite.

• But there are risks to understand when going too early.

Specht, a professor of agronomy and horticulture at UNL, says researchers in Iowa, Indiana and Wisconsin have documented similar yield penalties from delaying planting beyond early May.

He cites these three primary reasons why the yield potential of any soybean crop can be greatly enhanced by planting as early as reasonably possible:

•More sunlight. Early planting helps to ensure soybeans collect as much of the seasonally available solar radiation as possible because plants require the sunlight’s energy to convert carbon dioxide into carbohydrates, protein and oils.

With earlier planting, a soybean crop canopy will cover the ground sooner in the growing season, collecting nearly all of the incoming sunlight from that day forward, Specht explains.

Also, remember that day length increases from the spring equinox to the summer solstice. Later-planted soybeans won’t be able to collect as many hours of sunlight compared to earlier-planted soybeans.

•More available water. Early planting helps soybeans yield more because they transpire a greater fraction of the seasonally available water. There is a linear relationship between the amount of total water transpired by the crop and final crop yield.

The seasonally available water includes off-season rainfall that was stored as soil water prior to planting, plus all of the in-season rainfall. In addition to allowing plants to collect more seasonal solar energy for use in photosynthesis, early planting increases the yield potential by allowing the crop to use more of the seasonally available water for transpiration because less soil water is lost to evaporation.

Crop water use includes water lost via evaporation directly from the soil, as well as water lost as transpiration from leaves. Crop water-use efficiency can be improved by reducing evaporative water loss.

This means more water will be available for transpirational water loss. Early planting helps in this regard because cooler soil and air temperatures prevailing in late April or early May are much less conducive to soil water evaporation than temperatures in late May and early June.

•More plant stem nodes. Earlier planting helps soybeans produce as many plant stem nodes as possible. This is important because nodes are where the plant produces its flowers, then pods and ultimately seeds within those pods.

The rates of soybean germination and emergence are slower in the cooler soil temperatures that prevail during earlier plantings. Once soybean plants reach the V1 stage, temperature sensitivity of node accrual is much less. In general, earlier soybean planting can increase crop yield potential by allowing plants to generate more stem nodes and induce the beginning flower (R1) stage to occur nearer to the date of the summer solstice, Specht says.

The yield reward from early planting should not be used as a reason to plant seed into seedbeds that are too wet, Specht emphasizes. He also cautions to exercise good judgment relative to other seed planting practices.

Carlton writes from Lincoln.

Assess the danger of 3 key risks when deciding to plant beans early

While higher yields can be the reward for planting soybeans early, University of Nebraska Lincoln soybean expert James Specht emphasizes using common sense and assessing the potential risks when deciding when to plant your soybeans.

He suggests paying particular attention to the following three risks:

1. A late-spring killing frost. The probability of damage from a killing frost rises with late-April and early-May planting dates.

The key to assessing this risk is to think in terms of the expected date of emergence rather than planting date, since damage occurs when emerged soybean tissue is exposed to a freezing air temperature of 32 degrees F.

To learn more about the timing and probability of late-spring freezes in your local area, Specht suggests visiting the High Plains Regional Climate Center website at www.hprcc.unl.edu. Click on “Historical Climate Data Summaries,” select the red box representing the weather station closest to your area, then on the left side select “Spring Freeze Probabilities,” and then “Tabular Output.”

2. Germination failure. Specht says today’s soybean varieties have much greater germination cold tolerance than older varieties. Producers today can push the limits of early planting by sowing the new varieties into 40-degree-F rather than 50-degree-F soil seedbeds.

Germination failure in early planting is not so much due to cold temperature as it is from wet conditions coupled with cold temperatures immediately after planting. Soggy soil conditions, coupled with cooler temperatures that slow soybean seed germination, can provide an environment that gives pathogens more time to infect seedlings before they emerge.

Seed fungicide treatments protect against germination failure and seedling loss under such conditions, says Specht. Even if wet and cold conditions do not materialize, the potential yield reward that comes with a successful earlier soybean planting usually makes a fungicide seed treatment a worthwhile “insurance” cost, according to Specht.

3. Migration of overwintering bean leaf beetles. These beetles are attracted to the first emergent soybean seedlings of the growing season and feed on the leaves for a short time, mate, lay eggs in the soil around the base of soybean plants and then die. The hatched larvae feed on soybean roots.